1. Field of the Invention
The present invention relates in general to a video telephone system, and more particularly to a method and an apparatus for changing communication modes during communication between calling and called video telephone systems.
2. Description of the Related Art
A number of normal telephones may be connected to a single telephone network line which has a specific call number.
Even though several video telephones are connected to such a signal transmission line as a telephone network line, the respective telephones are capable of conducting transmission/reception of audio and video information to/from a counterpart video telephone via the telephone network line if the communication between the calling and called video telephones is carried out by using modulation and demodulation techniques. However, if the communication of information between the two video telephones over the telephone network line is achieved by the normal telephony communication technique, only voice communication is possible but not video communication. This is because the video signal transmitted via the telephone line is a digital signal. In other words, the telephone network line is inappropriate for transmitting the digital signal without its modulation, as is well known. Thus, for simultaneous transmission and reception of the audio and video signals via a telephone network line between a calling video telephone and a called video telephone, each video telephone must include a modem device for modulating and demodulating the audio and video signals.
An earlier method of performing video communication via a telephone network line between calling and called video telephones, each of which having a modem device comprises the steps of: calling the called video telephone via the telephone network line, in response to the key-inputted call number, determining whether or not an acknowledge signal is generated by the called video telephone; if so, performing voice communication with the called telephone; determining whether or not video communication is selected according to a consultation with the called telephone; if so, performing the video communication with the called telephone; determining whether or not there is a communication termination request from either the calling or called telephones; and if so, terminating the video communication of the calling video telephone with the called video telephone.
In the earlier method as stated above, video communication can be performed by simultaneously selecting the video communication mode at both video telephones during voice communication. If one of the video telephones is not set to the video communication mode, the video communication cannot be performed therebetween. Thus, so as to perform the video communication between the video telephones, both of them must be set to the visual communication mode.
Also, it is impossible to change a video communication mode to a voice communication mode during communication, and vice versa.